In optical communications, packages for an optical semiconductor device, such as the TO-46 package defined by JEDEC (the JEDEC Solid State Technology Association), are employed as packages for mounting a surface-emitting laser or a photodiode. According to common packages for an optical semiconductor device, leads (terminal parts) are inserted through holes formed through the package and are sealed with glass. Furthermore, according to packages for an optical semiconductor device, the characteristic impedance of a lead is matched to, for example, 50Ω per terminal to prevent a decrease in the efficiency of signal transmission during high-speed communications.
In packages for an optical semiconductor device, spatial restriction makes it difficult to enlarge a hole for inserting a lead to match the impedance per terminal to 50Ω. Therefore, consideration is given to decreasing the dielectric constant of sealing glass and reducing the wire diameter of a lead.
Reducing the wire diameter of a lead, however, not only makes the lead easily bendable but also prevents an area for wire boding from being created at the upper end of the lead. While the lead may be processed into a so-called “nail lead” that is wider at the upper end, the small wire diameter of the lead makes it difficult to perform stable processing.
Thus, there is a limit to the reduction of the wire diameter of a lead. Therefore, studies have been made of designing the shape of a lead to reduce the wire diameter in part of the lead.
Reference may be made to, for example, Japanese Laid-open Patent Publication No. 2009-105284 for related art.